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Segment Information (Reconciliation of Segment Results to Income Before Federal Income Tax (Details)) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Investment income, before federal income tax	$ 28,810	$ 41,313	$ 74,610	$ 84,065
Interest expense	(5,490)	(5,425)	(10,969)	(10,986)
General corporate and other expenses	(5,679)	(6,451)	(15,731)	(13,543)
Income before federal income tax	46,765	39,521	103,055	64,605
Standard Commercial Lines [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss), before federal income tax	35,241	15,703	65,277	12,073
Standard Personal Lines [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss), before federal income tax	(4,655)	(5,582)	(7,121)	(7,942)
Excess And Surplus Operations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss), before federal income tax	(1,462)	(37)	(3,011)	938
Operating Segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total all segments	$ 57,934	$ 51,397	$ 129,755	$ 89,134

X

- Definition

The income earned from investments in securities and other investments including dividends, interest, and returns on other investments, including realized gains/losses.

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Total of all reportable segments' income or loss from continuing operations, before federal income taxes.

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Net premiums earned and other insurance income less net loss and loss expenses incurred, loss adjustment expenses, policy acquisition costs and other underwriting expenses.

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef



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-Name Accounting Standards Codification



-Topic 940



-SubTopic 20



-Section 25



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Amount of general expenses not normally included in Other Operating Costs and Expenses.

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